Computing devices, for example navigation devices, which include Global Positioning System (GPS) signal reception and processing functionality are well known and are widely employed as in-car or other vehicle navigation systems.
In general terms, a modern navigation system comprises a processor, memory, and map data stored within said memory. The processor and memory cooperate to provide an execution environment in which a software operating system can be established, and additionally it is commonplace for one or more additional software programs to be provided to enable the functionality of the navigation system to be controlled, and to provide various other functions.
Typically, these devices further comprise one or more input interfaces that allow a user to interact with and control the device, and one or more output interfaces by means of which information may be relayed to the user. Illustrative examples of output interfaces include: a visual display and a speaker for audible output. Illustrative examples of input interfaces include: one or more physical buttons to control on/off operation or other features of the system (which buttons could be on a steering wheel), and a microphone for detecting user speech. In one particular arrangement, the output interface display may be configured as a touch sensitive display (by means of a touch sensitive overlay or otherwise) additionally to provide an input interface by means of which a user can operate the device through the display.
Devices of this type will also often include one or more physical connector interfaces by means of which power and optionally data signals can be transmitted to and received from the system, and optionally one or more wireless transmitters/receivers to allow communication over cellular telecommunications and other signal and data networks, for example Bluetooth, Wi-Fi, Wi-Max, GSM, UMTS and the like.
Navigation systems of this type also include or are coupled to a GPS antenna by means of which satellite-broadcast signals, including location data, can be received and subsequently processed to determine a current location of the system.
The navigation system may also include electronic gyroscopes and accelerometers which produce signals that can be processed to determine the current angular and linear acceleration, and in turn, and in conjunction with location information derived from the GPS signal, velocity and relative displacement of the device and thus the vehicle in which it is mounted. Typically, such features are most commonly provided in in-vehicle navigation systems.
In this respect, in recent years it has become common to integrate display devices into the dashboard of vehicles to support various systems, for example, entertainment systems, so-called “infotainment” systems, and/or navigation systems. Typically, in integrated systems of this type, the display module (or display screen) is located separately from one or more display drivers and other processing resources used to supply timing information, display information and to control the display module. Consequently, the display module and driver(s) are connected by means of a cable, for example a ribbon cable.
It is known that clock and data signals applied to the cable between the display driver(s) and the display module result in electromagnetic radiation being emitted from the cable. With the ever improving graphics capabilities of display screens, the rate at which clock and data signals are required to pass along the cable is also increasing, and thus the amount of electromagnetic radiation emissions is increasing too. In this respect, as the frequency of the clock signal increases, for example from about 10 MHz in previous generation systems to about 30 MHz, propagation of the faster clock signal over the cable connecting the display driver(s) and the display module results in an increase in the electromagnetic radiation emissions. In this respect, the clock signal is a repetitive and comprises multiple overtones constituting narrow band interference. The maximum frequency of the data signals is half the clock frequency and changes state randomly, resulting in significantly lower levels of electromagnetic radiation emissions that are spread over the frequency band. Generally speaking, an increase in the clock frequency by a factor x results in an increase in the emission of electromagnetic radiation by a factor of about x2.
In various industries, techniques are required to reduce the electromagnetic radiation emissions to an acceptable level. For example, in the automotive industry, strict requirements exist concerning permissible levels of electromagnetic radiation emission by electronic devices. In this respect, one exemplary standard is that set out by the Comité International Spécial des Perturbations Radioélectriques (CISPR) of the International Electrotechnical Commission (IEC), namely the CISPR-25 standard entitled “Radio disturbance characteristics for the protection of receivers used on board vehicles, boats, and on devices—Limits and methods of measurement”. This standard sets out techniques that can be used to limit electromagnetic radiation emissions, for example: clock and data line filtering; maintaining the distance between the driver and display module as short as possible, such as below 4 cm; providing shielding over or around the cable; making a low impendence ground connection between the driver, in particular the display driver Printed Circuit Board (PCB), and the display module; and physically integrating the driver with the display module.
However, reduction of the increased electromagnetic radiation emissions resulting from increased clock speeds to those required by, for example the automotive industry, using traditional methods described above is prohibitively costly. Without control of electromagnetic radiation emissions, however, malfunctions of other, possibly critical, in-vehicle systems may occur.